Transmission system, receiver, and decimation device

ABSTRACT

The invention presents a programmable communication system for generating data for at least one processing unit at a fixed symbol frequency, which lies within a range of frequencies, on the basis of input samples received at an input frequency higher than the symbol frequency. To achieve this, communication time slots are reserved periodically as a function of the maximum envisaged symbol frequency, and the device is designed for using only a fraction of these slots reserved as a function of the fixed symbol frequency for transmitting the generated data. The invention is applicable to broadband digital communications, digital television, channel decoding, demodulation and other similar technology areas.

FIELD OF THE INVENTION

The invention relates to a transmission system comprising at least atransmitter and a receiver, said receiver comprising decimation meansfor generating data at a symbol frequency on the basis of input sampleswhich have an input frequency higher than the symbol frequency, whileusing communication slots reserved periodically for transmitting thegenerated data.

It also relates to a receiver and a decimation device for generatingdata at a symbol frequency on the basis of input samples which have aninput frequency higher than the symbol frequency, while usingcommunication slots reserved periodically for transmitting the generateddata.

It has numerous applications, in particular in broadband digitalcommunication systems such as digital cable or satellite television.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 3,810,103 describes a dynamic communication system betweena transmitter and a receiver which uses acknowledgement means in theform of a transmission of flags to indicate whether the receiver isready to receive data, whether data have been transmitted by thetransmitter, and whether the receiver has correctly received thetransmitted data.

SUMMARY OF THE INVENTION

The present invention has for its object to provide a communicationsystem which is programmable as a function of the envisaged applicationand which has a static architecture, i.e. which can supportcommunications at various frequencies, but whose behavior is independentof the data to be transmitted, so that it can be easily validated. Thecited patent describes a system provided for dynamic communicationswhere the behavior is highly dependent on the transmitted data. Itaccordingly does not provide a solution to the problem posed by theinvention.

In multiple access transmission systems, several transmitters share thesame resource of a communication medium. In time division multipleaccess systems, time slots are reserved by the transmitters in order totransport their information data via the medium, towards the receiversaddressed. When all communications are known in advance, time slots maybe allocated according to a static pattern, for each transmitter. Thisprevents any conflict occurring. But when all communications are notpredictable, particularly when the output symbol frequency may vary intime, the totally static scheme is not usable any more.

An object of the invention is to introduce a degree of dynamism into anarchitecture of the static kind, in order to be able to generate variousoutput frequencies that may vary in time.

A transmission system, a receiver, and a decimation device according tothe invention and mentioned in the opening paragraphs are characterizedin that a fraction of said reserved slots is used for transmitting saiddata.

Decimation devices are well known in demodulators of digitaltransmission systems. They reduce the frequency of the received datathat have been previously over-sampled. Here, the term decimation deviceis employed in a very wide sense, to indicate any device which isdesigned to reduce the frequency of received data.

According to the invention, the frequency of received data is reduced byusing a fraction of reserved slots for transmitting the received data.

According to a major characteristic of the invention, the decimationdevice comprises means for transmitting a validity informationassociated with the data transmitted in said reserved slots.

Therefore, the data destined to be further processed are transmittedwith an extra information added, to indicate to further processingmembers whether the transmitted data are usable or not. The addition ofthis piece of information to the transmitted data allows to reduce thefrequency of said transmitted data without modifying the allocation planof the shared medium. When a slot contains an information flagindicating that the slot does not contain data to be processed, i.e.valid data, this slot is to be considered as if it does not contain anydata at all.

According to another characteristic, the decimation device beingdesigned to generate data at the symbol frequency to at least oneprocessing unit controlled by a control member, the invention ischaracterized in that said control member comprises detection means forsaid validity information so as to prevent the processing of associateddata by said processing unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description given with reference to the annexed drawings,all by way of non-limitative example, will render it clear how theinvention may be put into practice.

FIG. 1 is a block diagram showing an example of a receiver according tothe invention.

FIG. 2 is a diagram showing the various signals used in a receiveraccording to the invention.

FIG. 3 is a diagram showing a decimation device according to theinvention.

FIG. 4 shows an example of a transmission system according to theinvention.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is a simplified block diagram of a receiver according to theinvention. It comprises at least:

-   -   a receiver block 10 for receiving analog data and providing        samples at an input frequency fe,    -   a decimation block 11 for generating data at an output frequency        fs, with fs<fe, which is predetermined as a function of the        desired symbol frequency in the envisaged application, on the        basis of input samples received at the frequency fe,    -   a connection or communication link 12 for transferring the data        generated with the output frequency fs by the decimation device        11 to another component in the receiver, in particular to a data        processing unit 13.

The decimation device 11 is provided for generating data with the outputfrequency fs in time slots or periods reserved on the connection line 12in accordance with a previously defined periodic schedule. No conflictcan thus arise since the total of the communications is arranged inadvance. This static schedule can be used unchanged as long as thecalculation flow generated by the envisaged application is predictableand independent of the transmitted data. By contrast, if the calculationflow is not completely periodical because the symbol frequency may varyover a major range of values as a function of the envisaged application,the purely static schedule is no longer applicable.

It is accordingly the object of the invention to introduce a degree ofdynamism into an architecture of the static type so as to manage thesymbol frequencies of a large number of applications, such as cable orsatellite transmissions. To achieve this, the invention provides meansfor preventing the processing of the transmitted data, derived frominput samples, at the level of the processing members situateddownstream of the decimation device according to the invention, incertain predetermined communication time slots from among the reservedslots. To be able to comply with all requirements of the variousapplications as regards the symbol frequency at the output of thereceiver, the allocation frequency for the reserved time slots must bedetermined as a function of the maximum symbol frequency desired by thetotal of the envisaged applications. For cable transmissions, forexample, the maximum symbol frequency is equal to 7 MHz, and forsatellite transmissions it is equal to 32 MHz.

Once the reservation frequency of the communication slots has beendetermined as a function of the highest symbol frequency, the decimationdevice is provided so as to generate data in the reserved slots at asuitable frequency, this time as a function of the symbol frequencydemanded by the current application. To achieve this, the decimationdevice comprises means for reducing the output frequency of the validdata which are to be treated subsequently by processing members asdetermined by the application.

In a preferred embodiment of the invention which generates signalsrepresented diagrammatically in FIG. 2, the decimation device comprisesmeans for associating a flag, referred to as validity flag, to the datatransmitted in the reserved communication slots so as to indicate to themembers for subsequent processing whether the transmitted data are“valid”, i.e. can be used. The interest of the “valid” bit is that itrenders it possible to retain a static architecture in an application inwhich certain functions or calculations depend on the transmitted data.In the diagram of FIG. 2:

-   -   the signal VI_max represents the communication slots numbered t0        to t5 reserved in accordance with a periodic allocation schedule        as a function of the maximum symbol frequency envisaged,    -   the signal VI represents the “valid” flag associated with the        data transmitted in each communication slot,    -   the signal DATA represents the data, written D0 to D4,        transmitted towards processing members for which they are        destined.

Said processing members for which these data are destined in their turnmust be capable of detecting and decoding the “valid” flag. To achievethis, the decimation device may generate the “valid” flag in thefollowing manner:

-   -   if a valid data is transmitted or produced in the form of a        result which can be used by a processing member, the flag is        given, for example, the value 1,    -   on the other hand, if no result is produced or no data is        transmitted, the flag is given, for example, the value zero.

The flag follows the same path as the data for which it gives a validityindication. For example, the multiplexers do not distinguish between adata validated by a flag with value 1 and a non-valid data whose flag isat zero. The same holds for the registers. By contrast, the valid flagmay play a part in the data processing for the processing members orcalculation members provided with processors which function by means ofcontrol programs. The program then must be capable of detecting the flagso as to deliver an appropriate instruction to the relevant processingmember. In the case of a filter, for example, which receives dataaccompanied by a “non-valid” flag, the associated program will block theinstruction, so that the data are not processed.

FIG. 3 shows, by way of example of an application, a programmabledecimation device in an embodiment of the invention which isparticularly suitable for a digital television receiver or set top boxfor demodulating digital data frames received through varioustransmission channels, in particular by cable, satellite, radio waves,etc. The receiver comprises:

-   -   an analog/digital converter 31 for sampling an input signal at a        sampling frequency fe,    -   a first processing block 32 for processing the received samples        and delivering new samples at a frequency fw, fe being a        multiple of fw and fw<fe, which block comprises an anti-aliasing        filter for realizing a reduction by 2 of the input frequency of        the filter (the sampling frequency fe) and for avoiding the        aliasing problems introduced by the decimation,    -   an interpolation block 33 for realizing an incomplete decimation        of the input frequency fw and generating a frequency which is        double the symbol frequency fs,    -   a second processing block 34 comprising a Nyquist filter for        eliminating the inter-symbol interference introduced by the        decimation, and means for dividing by 2 for generating data at        the symbol frequency,    -   a phase locking loop PLL for realizing a counter-reaction 35        between the output of the Nyquist filter 34 and the interpolator        33 so as to adapt in real time the frequency generated by the        interpolator as a function of the frequency measured at the        output of the Nyquist filter and of the desired output frequency        fs.

In the embodiment shown by way of example in FIG. 3, the decimationdevice according to the invention is formed by the blocks 32, 33 and 34and the counter-reaction loop 35.

FIG. 4 is a general diagram of a transmission system according to theinvention comprising a transmitter 41, a receiver 42 of the type asshown in FIG. 1, and a transmission channel 43 which provides, forexample, satellite links, cable transmissions, radio waves, etc.

1. A transmission system comprising: at least a transmitter and areceiver, said receiver comprising a decimator for generating data at asymbol frequency based on input samples which have an input frequencyhigher than the symbol frequency, wherein the generated data istransmitted using a fraction of communication slots that are reservedperiodically based on a predicted maximum symbol frequency.
 2. Atransmission system as claimed in claim 1, wherein said decimatortransmits validity information associated with the data transmitted insaid reserved slots.
 3. A transmission system as claimed in claim 2, thedecimator generating data destined for at least one processing unitcontrolled by a control member, wherein said control member comprises adetector for detecting said validity information so as to preventprocessing of associated data by said processing unit.
 4. A receivercomprising: a decimator for generating data at a symbol frequency basedon input samples which have an input frequency higher than the symbolfrequency, wherein the generated data is transmitted using a fraction ofcommunication slots that are reserved periodically based on a predictedmaximum symbol frequency.
 5. A receiver as claimed in claim 4, whereinsaid decimator adds validity information to the data transmitted in saidreserved slots.
 6. A receiver as claimed in claim 5, the decimatorgenerating data at the symbol frequency for at least one processing unitcontrolled by a control member, wherein said control member comprises adetector for detecting said validity information so as to preventprocessing of associated data by said processing unit.
 7. A decimationdevice comprising: means for generating data at a symbol frequency basedon input samples which have an input frequency higher than the symbolfrequency, and means for processing the generated data, wherein thegenerated data is transmitted using a fraction of communication slotsthat are reserved periodically based on a predicted maximum symbolfrequency.
 8. A device as claimed in claim 7, wherein said devicecomprises means for transmitting validity information associated withthe data transmitted in said reserved slots.
 9. A device as claimed inclaim 8, the means for processing comprising at least one processingunit controlled by a control member, wherein said control membercomprises detection means for detecting said validity information so asto prevent processing of associated data by said processing unit.
 10. Amethod for operating a transmission system comprising at least atransmitter and a receiver, said method comprising the steps of:generating data in a decimator in said receiver at a symbol frequencybased on input samples which have an input frequency higher than thesymbol frequency; and transmitting the generated data using a fractionof communication slots that are reserved periodically based on apredicted maximum symbol frequency.
 11. A method as claimed in claim 10further comprising the step of: transmitting from said decimatorvalidity information associated with the data transmitted in saidreserved slots.
 12. A method as claimed in claim 11, whereintransmitting the generated data comprises transmitting the generateddata to at least one processing unit controlled by a control member,said data comprising said validity information, and further comprisingthe steps of: detecting said validity information in said controlmember; and preventing processing of associated data by said processingunit when said validity information is detected by said control member.13. A method as claimed in claim 10, said method further comprising thestep of: operating said transmission system in one of: a broadbanddigital communication application, a digital television application, achannel decoding application and a demodulation application.
 14. Amethod for operating a receiver comprising a decimator in a transmissionsystem, said method comprising the steps of: generating data in saiddecimator in said receiver at a symbol frequency based on input sampleswhich have an input frequency higher than the symbol frequency; andtransmitting the generated data using a fraction of communication slotsthat are reserved periodically based on a predicted maximum symbolfrequency.
 15. A method as claimed in claim 14 further comprising thestep of: transmitting from said decimator validity informationassociated with the data transmitted in said reserved slots.
 16. Amethod as claimed in claim 15, wherein transmitting the generated datacomprises transmitting the generated data to at least one processingunit controlled by a control member, said data comprising said validityinformation, and further comprising the steps of: detecting saidvalidity information in said control member; and preventing processingof associated data by said processing unit when said validityinformation is detected by said control member.
 17. A method as claimedin claim 14, said method further comprising the step of: operating saidtransmission system in one of: a broadband digital communicationapplication, a digital television application, a channel decodingapplication and a demodulation application.
 18. A method for operating adecimation device in a transmission system, said method comprising thesteps of: generating data in said decimation device at a symbolfrequency based on input samples which have an input frequency higherthan the symbol frequency; and transmitting the generated data using afraction of communication slots that are reserved periodically based ona predicted maximum symbol frequency.
 19. A method as claimed in claim18 further comprising the step of: transmitting from said decimationdevice validity information associated with the data transmitted in saidreserved slots.
 20. A method as claimed in claim 19, whereintransmitting the generated data comprises transmitting the generateddata to at least one processing unit controlled by a control member,said data comprising said validity information, and further comprisingthe steps of: detecting said validity information in said controlmember; and preventing processing of associated data by said processingunit when said validity information is detected by said control member.